 Dear students, in this topic we shall discuss the pheromones and chemical communication. The pheromones are the chemical messengers, which are released by many animals in the environment to communicate with each other. They are spread through the air and affect the behavior of individuals of a species. They are effective at remarkably low concentrations, they have particular orders and so they are detected by the olfactory receptors of the receiving animal. The chemical communication through pheromones is well developed in unicellular organisms, insects, fishes, salamanders and mammals. Dear students, now we shall discuss the roles of pheromones. The first role of pheromones is to recognize the members of one's own species. For example, unicellular organisms recognize the members of their own species. Many insects identify the members of their colony through pheromones. The pheromones also play certain reproductive roles. They attract the members of opposite sex for breeding. They induce courtship behaviors in the members of a species and also induce spawning behaviors in aquatic animals, which have external fertilization. In this way, spawning behavior means that eggs and sperms at a time release eggs and sperms. This is spawning behavior and is induced by pheromones. Pheromones also play a role in territorial behaviors. Many male members mark their territories with pheromones. They create pheromones to make their gait boundary. It warns other males that the area is occupied. Pheromones also play an important role in insects' social order development. In the honey bee colony, we see that pheromones, which produce a queen, that pheromone maintains the hive's complex social order consisting of worker bees, male and other queens. Pheromones are also used to give alarm calls. Most species' members release pheromones in the form of injures. It warns other members of the species about the presence of danger in the area. Pheromones are also used to repel predators. For example, skunks produce a very foul-smelling musk which is a pheromone and it makes these skunks unpalatable to their enemies. Dear students, now we shall discuss the advantages of pheromones as a chemical signal. Pheromones provide a simple message that can last for hours or days. They are equally effective during the night or day. They may be transported by air to long distances and they take relatively little energy to produce. However, these chemical signals have certain disadvantages. For example, they are comparatively slow to act and such a signal cannot be changed quickly.